Richard Bach. The Seagull named Jonathan Livingston (№ 10760)

Your whole body, from wingtip to wingtip, is nothing more than your thought itself, in a form you can see. Break the chains of your thought, and you break the chains of your body, too...
Your whole body from the tip of one wing to the tip of the other is nothing like your idea expressed in a form that is accessible to your vision. Break the chains of your thought, and you break the chains your body...